Thiol radical-based writable colormetric indicators†

Abstract

Efficiently and facilely indicating the spoilage of perishable products remains challenging. To address this issue, radicals are utilized for the first time as molecular probes to monitor the surrounding environment of perishable products. The colorimetric indicators, composed of molecular probes, utilize radicals to monitor environmental factors such as oxygen, water, and temperature through their quenching process in the environment, accompanied by color changes. The quenching dynamics of phenylthiol radicals are systematically decoded, revealing their inherent functionality as sensitive environmental probes for real-time monitoring of quenching in perishable foods, vaccines, biological samples, and other items during their storage and transportation. The immobilized phenylthiol radicals on rigid cross-linked polymer particles exhibit tunable chromatic responses to multiple stimuli (O₂, H₂O, and temperature), while the solvent-free fabrication allows on-demand creation of customizable colorimetric patterns. The irreversible quenching process of radicals imparts tamper-resistance to colorimetric indicators. This work establishes a new paradigm for developing multifunctional radical indicators with enhanced sensitivity and practical applicability in smart packaging and biomedical monitoring.